The rendering drinkable of a water can be carried out either by a solely mechanical means, that is by passage of water through a filtering unit, or by mechanical and chemical means, that is by filtration combined with the action of chemical products on the materials in suspension.
Individual devices exist which are conceived to respond to these needs, but their performances are limited. The first group are apparatuses equipped with filter candles. The filtration unit is composed of one or several porcelain candles with controlled porosity. The filtration takes place from the exterior of the candle towards the interior. Clogging of the candle is rapid and the filtration output is very low (less than one to a few liters per hour). Other apparatuses are equipped with filtration membranes or cartridges. The operating principle of these apparatuses resides in the passage of the water through one or several microfiltration membranes. However, these devices clog easily and are ineffective with regard to chemical and bacterial pollution.